The £5 coin is available in silver - because the crossing of a baby's palm with silver is said to confer good health and prosperity to newborns - and gold - to commemorate the royal celebration.

William and Kate's son will be christened at the Chapel Royal, St James's Palace on October 23.

Dr Kevin Clancy, director of the Royal Mint Museum, said the coin's designer, John Bergdahl, has created something "timeless.

"It's symbolic and it's got dignity about it," he said.

"We've had to bring the royal couple along with us on this. The Duke and Duchess of Cambridge have been involved in the approval of the theme."

He said the Queen and Chancellor George Osborne had also given the design their approval.

Mr Bergdahl said: "The design is baroque, a style that has been reborn many times and often featured in royal artwork and traditions.

"One element that I knew I wanted to incorporate was the Lily Font from the Tower of London, which is a strong tradition in christenings for the Royal Family.

"The motto is traditional and sums up the expectation carried by a young child, born to reign - regardless of gender - for the first time ever."

Mr Bergdahl said it normally takes up to two years to produce a new coin, but the christening edition had to be made in around seven months because of the unknown details about the royal baby, such as its gender or name.

"Hopefully it will be timeless and it will still look as good in 100 years' time as it does now," he added.

The prince has already had coins minted in his honour. The Royal Mint gave away 2,013 silver pennies to babies born on the same day as the duke and duchess's son.